50*50-49*49+48*48.+2*2-1*1

问题描述:

50*50-49*49+48*48.+2*2-1*1

50*50-49*49+48*48.+2*2-1*1
=(50+49)(50-49)+(48+47)(48-47)+-----+(2+1)(2-1)
=50+49+48+47+-------+2+1
=(50+1)*50/2
=1275